The present invention relates to photoelectric encoders. The present invention relates, in particular, to, for example, photoelectric encoders of a light transmission type and a light reflection type employing a moving object with a plurality of slits formed.
The present invention also relates to electronic equipment provided with such a photoelectric encoder. The electronic equipment widely includes printing machines such as copying machines and printers and FA (Factory Automation) equipment such as robots.
As this kind of photoelectric encoder, a light transmission type as shown in FIG. 12A in which a light-emitting section 101 and a light-receiving section 102 are arranged facing each other, and an output is obtained by making a moving object 103 that has a plurality of slits formed pass between the light-emitting section 101 and the light-receiving section 102, and a light reflection type as shown in FIG. 12B in which a light-emitting section 201 and a light-receiving section 202 are arranged side by side, and an output is obtained by making a moving object 203 that has a plurality of slits formed pass through positions opposite to the light-emitting section 201 and the light-receiving section 202 are known.
The photoelectric encoder of the light transmission type often has a moving object 40, which has a plurality of slits X1, X2, . . . at a constant pitch P in the movement direction and whose slit width is 1/2 pitch (i.e., P/2) as schematically shown at the top of FIG. 11 between the light-emitting device and the light-receiving device arranged facing each other. In the light transmission type, the slits X1, X2, . . . correspond to portions (referred to as a “light-on portion”) that make light incident on the light-receiving device, and portions Y1, Y2, . . . constructed of a plate material (material of moving object) located between the slits X1, X2, . . . correspond to portions (referred to as a “light-off portion”) that does not make light incident on the light-receiving device.
For example, in the device described in JP 3256109, as shown in the middle of FIG. 11, four photodiodes PD1, PD2, PD3 and PD4 whose width is a half (i.e., P/4) of each slit width are arranged without spacing along the direction in which the slits X1, X2, . . . of the moving object 40 are arranged, and four signals (assumed to be A+, B−, A− and B+ in a sequence) outputted from the photodiodes PD1, PD2, PD3 and PD4 are read. By comparison between A+ and A− and between B+ and B− of these four signals by respective comparators, two output signals whose phases are mutually different by 90° are obtained.
Moreover, in the device of JP 2001-99684 A, as shown at the bottom of FIG. 11, four photodiodes 13a, 13b, 13c and 13d whose width is equal (i.e., P/2) to the slit width are arranged at 3/4 pitch (i.e., 3P/4) along the direction in which the slits X1, X2, . . . of the moving object 40 are arranged, and four signals (assumed to be A+, B+, A− and B− in a sequence) outputted from the photodiodes 13a, 13b, 13c and 13d are read. By comparison between A+ and A− and between B+ and B− of these four signals by respective comparators, two output signals whose phases are mutually different by 90° are obtained.